Process for changing solubility of cellulose acetate



Sept. 20, 1932. 1,878,953

PROCESS FOR CHANGING SOLUBILITY OF GELLULOSE ACETATE c. J. MALM Filed Dec. 12. 1928 H QQQ R attozmq Patented Sept. 20, 1932 UNITED STATES,

PATENT orrlcs CARL 3. MALE, OF ROCHESTER, YORK, ASSIGNOR TO EASTMAN KOD AK COKPANY,

OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK PROOESSFOR CHANGING SOLO'BILITY OF CELL'O'LOSE ACETATE Application filed December 12, 1928. Serial No. 325,597.

This invention relates to a process for the I deacetylation, to any desired degree, of .chloroform soluble cellulose acetate, cellulose triacetate, and to the product of such deacetylation. I

Among the objects of the invention are the accom lishment of the-deacetylation without degra ation of the cellulose molecule; regulation of the rate of deacetylation so that it is uniform throughout the reaction mixture; accurate determination and control of the extent of the reaction so that it can be stopped at a precisely defined point; and the obtaining of products having qualities rendering them particularly desirable for selected uses,

\ and particularly for photographic purposes.

Other objects will appear hereinafter.

There are three essential steps in the manufacture of cellulose acetate. The first step comprises preparing the cellulose fibre as by treating it with reagents which so aifect the fibre that subsequent acetylation is facilitated and more easily controlled. Examples of such pretreating methods are described in U.

5. Patent 854,374, Mork, May 21, 1907. The

second step covers the acetylation of the cellulose as with acetic acid, acetic anhydride and. a catalyst; the reaction being ordinarily conducted at temperatures below 40 C., until a cellulose acetate is produced which has the desired solubility in chloroform. This step may be conducted in accordance with the disclosure in U. S.- Patent 1,591,590, Webb &

Malm, July 6, 1927. Both steps may be conducted in accordance with the patent to Gray eggs Stan d, No. 1,683,347, granted Sept. 4, Cellulose acetate of the chloroform soluble type produced as described above is not particularly suited for many industrial processes,

such as the manufacture of photographic film or rayon. It has been found that prod-.

ucts having solubility in acetone have many advantages, This is accomplished by the third step, hydrolysis or deacetylation, which may be carried out as described in U. S Patent 1,635,026, Baybutt'& Farrow, July 5, 1927. This process is also termed saponification.

It is well known in this art that if the second step cellulose acetate is hydrolyzed by a the cellulose the usual methods employed, it is very diflicult for an operator consistently to obtain consecutive batches of partly deacetylated cellulose acetate that will meet the requirements of rigid manufacturing tolerances. I have found, on theother hand, that by' using my hydrolyzing method the operator can consistently and accurately produce a product that will conform to those tolerances. The prior art also teaches that the time of hydrolysis is affected by the temperature of the hydrolyzing bath. The higher the temerature the greater the rate of hydrolysis. t also teaches that continuance of the process at the higher temperatures customarily employed beyond a period such as 24 to 48 hours results in an inferior product, due to the breakdown or degradation of the cellulosemolecule. It further teaches the use of relatively large uantities of mineral acid in the hydrolyzing ath. This results m a gradual degradation of the cellulose molecule as the deacetylation proceeds.

The possible reactions taking place in the hydrolyzing bath are as follows;

1. The splitting off of acetyl groups wh1ch is'termed deacetylation or saponification.

2; The decrease in molecular magnitude of the cellulose molecule, which may be termed degradation.

This degradation isindicated or measured by'its tetrachlorethane viscosity, this being a known test described in Advisory Committee for Aeronautics, Dec. 1918, Report and Memorandum #568see Figure 16, and bea ing the tetrachlorethane viscosity of the ma- I terial, after complete reacetylatlon, this being compared withthe tetrachlorethane vlscosity of the cellulose triacetate from whlch the deacetylated material was produced. It may also be indicated or measured by its cupro-ammonium viscosity, thls being a known'test described in Joyner, J. C. S., London, vol. 121, page 1523, and being the cuproammonium viscosity of the maternal after 95 complete .de-esterification, this belng compared with the cupro-ammomum viscosity of triacetate, after complete deesterification, from which it was produced.

The optimum result in the conversion of 7 t tion of these factors and particularly by so cellulose acetate to an acetone soluble form for many purposes, and particularly for photographic purposes, is attained when the deacetylation is so conducted as to preclude simultaneous degradation of the; cellulosemolecule. As noted above, in all-previous processes, saponification or deacetylation has been accompanied by a marked degradation. The following factors afiect the extent and the actual and relative rates of reactions:

1. Temperature. 2. Concentration of mineral .acid. 7 3. Ratio of solvent to solute. 4. Time. I have found that it is possible to attain the desired optimum result by suitable selecselecting them that the rate of deacetylation is low and consequently the periods of time required for the reaction are much greater than has hitherto been employed.

Favorable conditions for attaining this result are found in the choice of low temperaitluria1 or low mineral acid concentration or I have found that the hydrolyzing bath best suited to carr out my process may consist of an excess 0 acetic acid over the cellulose acetate contained therein of approximately 700%. A smaller or larger excess,

however, would not appreciably aflect the percentage.

proven very satisfactory and is preferably results although I prefer to use the above The mineral acid catalyst has used at an extremely low concentration, say

from of 1%.to not more than 1%. 1f other catalysts are to be used such as phenol sulfonic acid, the acid sulfites, or the sulfur ports in this art, will give the correct pro'por-' the appended claims.

chlorides,'the ratio oftheir' catalytic reactivity to the mineral acids, known to the expatent, 500 parts of substantially glacial acetic acid, and approximately 1 part of sulfuric acid and 3 parts of phosphoric acid, is

added a mixtureof 37 part's'of water and .60 parts of glacial acetic acid. There results a solution of. 80 parts of cellulose triacetate in 597 parts of 94% aceticacid with less than V of 1% of sulfuric acid and less than /-,of1% of phosphoric acid. This mixture is maintained at a temperature of F. for at least 15 days and then precipitated into water or dilute acid the product obtained'has maximum acetyl content of 41.5%.

The reaction may run for from fifteen to a hundred days, during which timethe deacet lation w1ll proceed at a substantially uni orm rate, and there will be no perceptible degradation .even at the end of this prolon ed period. This I consider a very remarka le 70 and unexpected result.

The physical and chemical properties of the-acetate are found to vary in a non-uniform manner throughout the reaction and by a determination of these properties it is.

possible to obtain an acetate having the desired properties or combination of properties by stopping the reaction at thepoint where these are most closely approximated. Be-

cause of the low rate of change of the propso erties it is possible to select wlth a very high degree of exactness the precise point at which to stop the reaction to obtain the desired properties.

By way .of illustration, the resistanceto 5 moisture at the beginning is extremely high and this gradually decreases at an increasing rate through the reaction until the acetate approaches or reaches water solubility. It is .still very "high after thirty-five days and at the end of the fiftieth day is moderately high. The resistance to deacetylation in alkah is high at the start and also slowly decreases.

The solubility in acetone is inappreciable v until about the fifteenth day. At this time 05 the acetone viscosity'is high and falls off very rapidly, reaching a minimum between the twentieth andtwenty-fifth day and then rising at a substantially uniform rate being'moderately high at the fiftieth day, and increasing very rapidly thereafter.

v The flexibility, asdetermined from a film coated from a solution of the acetate in acetone, rises fromzero at fifteen days-to a very sharp maximum at about thirty days, after which it drops somewhat passing through a minimum of moderate flexibility at about" forty days, and thereafter rising and remaining above its first maximum. e

Thewhole period may, for convenience for purposes of discussion, be divided up into periods, but it is'to be understood, that there areno sharp breaks in the process nor in the properties of the products. 4 I

these perlods may 116 .In'the above example, be defined as follows 4 Period I. First to fifteenth day. The acetyl content is gradually reduced from 44.8% to 41.5%. This period is of little interest for the purposes of this application, but 120 it may be stated that if an attempt is made to shorten it by raising the temperature to,

say, 120 F. there is'noticeable molecular.

degradation.

I Period IL. Fifteenth to twentieth day.

During this period the acetyl content falls from 41.5% to 41% the resistance to moisture and to deacetylation in alkali remain very high, though decreasing very slightly, the

acetone viscosity is high, but falling rapidly.

- hundred days.

four days, five and one-half days,

. Example 1 would not be Period III. Twentieth to twenty-seventh day. The acetyl content falls from 41% to 40.5%; the resistance to moisture and to deacetylation in alkali remain very high though decreasing slightly, acetone viscosity passes through a minimum, flexibility increases rapidly.

Period IV. Twenty-seventh to thirtythird day. Acetyl content falls from 40.5 to 40%.

continues high but decreasing; acetone viscosity is low but rising steadily, flexibility is high and passes through a maximum- Period V. Thirty-thirdsto fiftieth day. Acetyl content falls from 40% to 38%, resistance to moisture and alkali fall with increasing rapidity but are moderately high. Acetone viscosity rises steadily and flexibility becomes somewhat less in the first part of the p'eriod'and then rises somewhat, being moderately high throughout.

Period VI. Beyond fiftieth day. Acetyl content decreases, being about 34% at'one Resistance to moisture and alkali decrease rapidly. Acetone viscosity rapidly increases, becoming extremely high. gleiribility increases and then remains very Example 2.-This is identical with example 1, except that a temperature of F. is maintained. In this case the points corresponding to the ends of the periods outlined above are eleven days, and one-half days, seventeen days, twenty I days and forty days.

E mample 3.This differs from the preceding in that a temperature of F. is maintained. The points corresponding to the ends of the described periods are approximately seven days, nine and one-half days, fourteen days, twenty-five days.

Example 1;.-This differs from the preceding in that a tem erature of F. is ma ntained. The points corresponding to the ends of the described periods are approximately 80 hours, 100 hours, hours, 160 hours, 200 hours. and 350 hours.

Example 5.-The hydrolysis is conducted in the same manner as in any one of the above examples. The starting material, however, is a chloroform soluble acetate made by a method using only sulfuric acid as a catalyst,

and hence the phosphoric acid mentioned in present. The proportions would otherwise be the same.

From the description of my invention contained in this specification, it will be observed that the greatest range of usefulness of my novel cellulose acetate lies within the range of periods majority of purposes, the hydrolysis of the cellulose acetate may conveniently be-stopped some time in periodsIII, IV and V. I have found that a cellulose acetate prepared in Resistance to moisture and alkali thirteen days, fourteen II to VI and that, for probably a g accordance with my invention and having a precipitation value ranging from ap roximately' 85% to approximately 98 o and which is soluble in acetone, hascthe greatest range of utility for the purposes specified herein. For some purposes, an acetate havin a precipitation value ranging between 90 0 to 96% is satisfactory. As above explained, the hydrolysis may be stopped at any desired period and when the desired precipitation value is reached This precipitation value is the percentage of cellulose acetate, which, from an acetone solution thereof, will precipitate in a mixture of 40% water and 60% acetone by value. i

In order that the method of determining this precipitation value may be more thoroughly understood, the exact method of determining it is described as follows:

Five grams of the dry cellulose acetate are accurately weighed and placed in a wide mouth 12 oz. bottle. To this are added 100 cc. of acetone (commercial grade of 99% or better), and the mixture is stirred until homogeneous. (The bottle the stirring with a rubber stopper fitted with a shaft for the stirrer). To this dope is added slowly from a pipette stirring,

.cc. of a mixture consisting of 2 parts of distilled water and 1 part acetoneby volume. Care, should be taken to keep the solvents and mixtures at 20 C. wherever volumes are being measured.

At the end of-the addition of the acetonewater mixture, a mixture is obtained containing 40% Water by volume (neglecting contraction) cipitated acetate. This is allowedto stand for 12 hours at 20 C. 25 cc. of the clearest portion (supernatant solution) are removed with a pipette. At the end of this time preci'pitationhas reached equilibrium and proceeds no further, and during the same time settling of the precipitate occurs. This 25 cc.

,is centrifuged in stoppered bottles at high speed until the liquid is perfectly clear. Ex-' actly 5 cc. of the clear liquid are removed with a pipette and evaporated to dryness on a. tared watch glass. If W is the weight of the residue in grams the precipitation value which equals the per cent acetate precipi- In the claims wherein precipitation value it is intended that the value is referred to, defined shall be one determined by the foreoing method.

used in the deacetylation bath, the maintained temperature of 100 F. will result in degradation. As the percentage is increased,

Cal

and with thorough in which is suspended the pre- If a high percentage of mineral acid is the operating temperature must necessarily be lower, and at considerable concentrations must be well below 50 F. to prevent degradation. The time at these lower temperatures will be so prolonged, that the process, while operative, is not well adapted for commercial exploitation.

It is, in general, an objection to this process that it requires a large expenditure for' suitable receptacles for the storage of the mate rial during the reaction. The advantages derived through accurate control, which result in uniform final products, more than offset, however, this disadvanta e.

In the accompanying rawing is shown a chart illustrating on purely arbitrary scales the changes in the properties during the continuance of the reaction. This is understood to be by way of example. Obviously it is impossible to place quantitative values on the graph or diagram as quantitative conditions are changed by a change in the temperature used. However the curves shown will be of 'the same order for each particular exam le of the process. The diagram is to be undiarstood as illustrative and not absolute.

If the dia-gramis taken as illustrative of Example 1, the periods are as disclosed on pages 7 and 8. As shown on the diagram the acetyl content decreases sharply the first period and more gradually in the'subsequent markedly after the fourth period, the acetone viscosity decreases abruptly in the first three periods, rises gradually during the fourth and fifth periods and then abruptly during the sixth period. In" the diagram as applied to Example 1 the six periods: cover a period of 100 days, as to Example II, 40 days, etc. Obviously certain .of the curves may be shifted in relative position or in degree by variation in the initial triacetate, proportions of the initial constituents of the bath,- the particular acid used and other detailsof the proc- For motion plcture film, particularly foi' projection purposes, where flexibility is a prime consideration, Periods IV, V, VI, are indicated as the best points, and particularly IV, since the film can then be easily formed and also has high resistance to the photographic baths.

For artifical silk, the particular point to the moisture resistance decreasespurpose, thev reaction be selected wouldbe determined by the in- I tended use. Since existing machines are designed partlcularl of high viscosity, Periods VII and are inthread-forming" for dope and washing is important, Periods. II,"III,

and IV are indicated. 7

For lacquers and varnish for nera-l use or forv coating motion picture high impermeability and hardness are de-' sirable, SectionsIII and IV would be selected,

while, for anti-static backing for motion pic'- ture film, Section VI would furnish theimost also be made from the material. VI, while, for. plastic work and could be selected.

Although I have included a sion of the results at the various-periods, some naturally are ofgreater value than' others and in this application the products resultin from stopping the reaction at Periods'II IV, and V are especially emphasized. j

m', where It is also to be noted that in thepreferred process in which the pretreatment and acetylation are carried out in accordanoewith-the Gray and Staud patent, there is present. in all the steps at least as much as there is sulfuric acid.

is nota part of my invention butis the: in-

vention of Albert F. Sulzer as set forth. and

phosphoric acid I Sheeting containing or prepared from the. cellulose acetate herein described andzclaimed claimed in Patent'No. 1,833,136 granted No vember 24, 1931. Similarly, artificial silk or' filaments containing or prepared from. the w .celluloseacetateherein describedand claimed is not my invention but is the invention of Paul C. Seelas application, Serial No. 416,286,-filed- December24,1929. r T I Having thus described my invention, what set forth and claimed in his I claim as new and desire to'secure by Leters Patent is:

.1. The method of treating-cellulose tri 7' acetate having an acetyl content. of the order of 44.8 until said acetyl content isof the that' compriscssubmitting it to' order to 40% a hydrolyzing bath comprising an excess of acetic acid and water, sulfuric acid and phosphoric acid, the amount of the sulfuric acid being of the order *fof of 1% and the phosphoric acid being i bfthe order of of 1% of the bath.

. 2 The method-of. treating cellulose-triacetate having an acetyl content-of-the order of 44.8% until saidacetyl contentis-of the order of40% thatcomprises submitting it to -a hydrolyizing' bath com rimng an excess of" said bath" containing:

' sulfuric acid'and phosphoric, the amount of. the sulfuric acid being of the order of'% of acetic acid and water,

said) bath containing desirable qualities. Sizes for: apercould I m'PeriOd i for'coatip'gf paper with an acetate layer, Periods V o'r-I 1% of the bath, and at a temperature not over 105 F. for a period of over 5 days.

' cent and submitting the triacetate to such bath for a period of time exceeding 4 days at a temperature less than 105 F.

4. In a process for making cellulose acetate including the acetylation of cellulose in the presence of sulfuric and phosphoric acids,

the method of hydrolyzing the triacetate thus formed that comprises the diluting of the acetylating bath to destroy the acetic anhydride, the mineral acid concentration being less than 1% and the continuance of the hydrolyzation at a temperature not greater than 105 F. for at least five days.

5. A process of making acetate by the successive steps of pretreatment, acetylation and hydrolyzation characterized in that there are present sulfuric acid and phosphoric acid during each of the three steps and that in the hydrolyzation steps the mineral acid concentration of the bath is less than one percent and that hydrolyzation is continued for at days.

least five days at a temperature not exceeding 105 F,

6. A process of making cellulose acetate by the successive steps of pretreatment, acetylabath containing a fraction of 1%. of a hydrolyzing catalyst for a period exceeding 6 days.

12. A processof de-acetylating a fully esterified cellulose acetate 'which comprises hydrolyzing the acetate in a bath containing an appreciable amount but less than 1% of sulfuric acid for a period exceeding 6 days.

13. A process of de-a'cetylating a. fully esterified cellulose acetate which comprises hydrolyzing the acetate in a bath containing an appreciable amount but not more than of 1% of sulfuric acid for a period exceeding 6 days.

14: A process of de-acet lating a substantially fully .estarified cellu ose acetate which comprises treating theacetate with a hydrolyzing bath until ithas a precipitation value of -98%. v

15. A process of de-acetylating a substantially fully esterified cellulose acetate which comprises treating the acetate with a hydrolyzing bath until it has a precipitation value of -96% Signed at Rochester, New York this 4th day of December 1928.

' CARL J. MALM.

tion and hydrolyzation characterized in that there are present sulfuric and phosphoric. acids during each of the three steps, the amount of phosphoric acid being at least as great as the amount of sulfuric acid and the hydrolysis being conducted for at least four 7. A process of making cellulose acetate by the successive steps of pretreatment, acetlylation and hydrolyzation characterized in that there are present sulfuric and phosphoric acids during each of the three steps, the amount of phosphoric acid being at least as great as the amount of sulfuric acid, and that hydrolyzation is continued. for at least five days at a temperature not'exceeding 105 F.

- 8. Cellulose acetate which is soluble in acetone and which has a precipitation value rang ing between 85% and 98%.

9. Cellulose acetate which is soluble in acetone and which has a precipitation value ranging between 90% to 96%.

10. A process of de-acetylating a substantially fully esterified cellulose acetate which comprises hydrolyzing the acetate 'in a bath containing from to 1% of a hydrolyzing catalyst for a period exceeding 6 days.

11. A process of de-acetylating a fully esterified cellulose acetate which comprises .5 hydrolyzing the acetate in an aqueous acid 6 v CERTIFICATE til-common.

mm. No. 1,818,953. $ep t emher 20, 1932.

' p a Y can]. mm.

It is hereby. certified that ei'rar appears in the printed spec fication of the "above numbered, patent repairing correction as follows: Page 3, line 80, for 'valne"-- read volume"; page 4', line 116, claim I, for "to" first oecurtenee;

read;'."ot"; and that .the said Letters Patent should'be read with these corree-- tions therein that the same may conform .to the record of the Icaae in the Patent Ottice. Y

Signed and'sealed this 6th day pi Deeedger, A.- D. 1932;

y mama, (Seal) Acting Gon'miaaioner of Patents. 

